There are a growing number of case reports which indicate that monoamine oxidase inhibitors may be helpful in patients with obsessive compulsive disorder (OCD). In addition, fluoxetine, a serotonergic antidepressant, was recently introduced on the United States market. Preliminary evidence indicates that fluoxetine may have antiobsessional effects. In our proposed study, we will compare the monoamine oxidase inhibitor, phenelzine, to fluoxetine to placebo in a randomized three-cell design in 75 patients meeting criteria for obsessive compulsive disorder. Measures of OCD, depression, and anxiety symptoms, as well as standardized assessment of DSM III Axis II disorders will be performed over the course of the 10 week study. At the end of the study we will determine if associated features (i.e., history of panic attacks, presence and type of Axis II personality disorder, abnormal DST) are related to treatment response to either drug.